1. Field of the Invention
The present invention relates to a vane pump suitable for use in a power steering system.
2. Description of the Prior Art
Conventionally is known a vane pump wherein a rotor having plural vanes is rotated within a cam ring received within a pump housing. In such vane pump, the vanes are supported slidably in radial directions so as to contact with an internal cam surface of the cam ring, so that plural pump sectors are defined between the rotor and the cam ring. When the rotor is rotated, volume of each pump sector changes in accordance with the cam curve of the internal cam surface so as to intake fluid from intake ports and to discharge pressurized fluid to exhaust ports.
The pressure of the fluid discharged from such pump pulsates due to the shape of the internal cam surface and leakage amount of the fluid from the pump sectors. To reduce such pressure pulsation of the discharged fluid, it has been tried to modify the curve of the internal cam surface. Although the pressure pulsation of the discharged fluid can be reduced by the modification of the cam curve, it was difficult to reduce the pressure pulsation to a required value. The pressure pulsation of the discharged fluid causes the pump and connection pipes connected to the pump to generate vibrations and noises. There is a power steering system wherein an accumulator is provided in order to absorb the pressure pulsation. However, such system has disadvantages such as component increase, cost increase.